The changes involved in adapting a generic mammalian template into a whale are certainly not all simple, independent, single-letter changes.
A bottleneck of two, or a first pair at our origin older than 500,000 years, is possible.
Once upon a time, a cell became a tumor. Animals were soon to follow.
Recently Dennis Venema joined with Scot McKnight to publish a book, Adam and the Genome, in which they claim that there never was an original pair of humans like Adam and Eve.
We have our Kremlinologists who observe the BioLogos website for hints of what ideas, and which people, are up or down in the world of theistic evolution.